Trichothecenes epoxide opening

Competition between an alkene and an ether oxygen for participation in epoxide opening is evident in the reactions of trichothecenes (illustrated by the skeletal structure 20 equation 8). In aqueous acid, participation of the ether oxygen is favored and (21) is formed, probably due to preferred cleavage at the tertiary center under the more electrophilic conditions. Under neutral or basic conditions, the diminished role of intermolecular electrophile (water) results in unusual scission of the primary epoxide bond, with formation of (22). ... 

Biological effects of trichothecenes depend on their structural integrity. Previous studies (Bamburg, 1976) have shown that opening the epoxide ring(s) present in all trichothecene molecules essentially abolishes their toxic properties. Modification... 

Recognised may be two additional trichothecene types. The type E trichothecenes include mycotoxins with an opened macrocyclic ring and the type F trichothecenes do not have the 12,13 epoxide ring as it is replaced by a vinyl linkage with the oxygen atom in the epoxide ring removed. 

---